NEW BEDFORD — A set of anti-fish barriers marked by an orange boom, white buoys and a stream of bubbles in the water is the first serious sign that momentum on the South Terminal project is scaling up.

NATALIE SHERMAN

NEW BEDFORD — A set of anti-fish barriers marked by an orange boom, white buoys and a stream of bubbles in the water is the first serious sign that momentum on the South Terminal project is scaling up.

The barriers, part of the environmental measures associated with the port development project, were installed the weekend of Jan. 12 and 13 in New Bedford Harbor, running roughly from the Schuster Corp. building to the Gifford Street boat ramps, said Assistant Harbormaster Victor Fonseca.

They alert boaters to a thinly woven net that drops almost to the bottom and is meant to keep winter flounder from releasing their eggs in the area and a silt curtain designed to contain materials disturbed during the construction, Fonseca said. Boats can pass to the boat ramp through an opening of about 75 feet cut off from the fish with a stream of bubbles pumped by underwater hoses.

"This is the first physical step towards that offshore wind energy future for Massachusetts," said Catherine Williams, a spokeswoman for the Massachusetts Clean Energy Center, which is in charge of the project. "It's a great sign of things to come."

The state is pushing for the Marine Commerce Terminal, currently out to bid, to be completed in about 19 months once it starts.

The anti-fish barriers will be in place for at least a year, Fonseca said. The mitigation measures cost about $200,000, Williams said.

Winter flounder — also known as lemon sole — spawn in shallow, sheltered areas in estuaries, said Vincent Manfredi of the Division of Marine Fisheries, which was consulted on the project. The fish drop their eggs when temperatures appear to start warming again, he said.

The eggs hatch between 30 and 60 days later; the young flounder spend the summer eating and growing, benefiting from the warmer water temperatures and more abundant food in the estuary, he said.

"The Acushnet River-New Bedford Harbor system is the largest river system that we have emptying into the bay," Manfredi said. "It would be considered habitat important to juvenile winter flounder."

As part of the mitigation efforts, the state is also creating about 23 acres of new winter flounder habitat in the outer harbor as part of its environmental protection measures, making those waters shallower to compensate for the deeper channels carved for the new terminal.

The population of winter flounder in New England and the mid-Atlantic is estimated to be at about 16 percent of what is needed to support a commercial fishery, according to NOAA. Flat fish are one of the dominant fish species in the harbor, according to EPA documents.

There has been no official, comprehensive survey of winter flounder population in New Bedford Harbor recently, but the species has been observed there by researchers, Manfredi said.

State and federal safety guidelines have ruled that flounder found in the inner and outer harbors are not safe to eat. That hasn't stopped the seals, which Fonseca said he had seen lunching on the bottom dwellers.